Process for preparing AlH3 (PO4)2 ·3H2 O

ABSTRACT

Crystalline AlH 3  (PO 4 ) 2  ·3H 2  O is obtained from an aqueous solution of aluminum phosphate containing a molar ratio of Al 2  O 3  :P 2  O 5  of from 1:2 to 1:6 and an organic solvent that is miscible with water. Crystallization is enhanced by the addition of AlH 3  (PO 4 ) 2  ·3H 2  O seed crystals to the aqueous solution. The product is useful in reducing the setting time of hydraulic binders.

This application is a continuation-in-part of application Ser. No.543,496, filed Jan. 23, 1975 (now U.S. Pat. No. 4,021,528).

The present invention relates to a process for preparing crystallineAlH₃ (PO₄)₂ ·3H₂ O from a solution comprising water, an organic solventmiscible with water and an aluminum phosphate.

It is already known that small quantities of AlH₃ (PO₄)₂ ·3H₂ O areformed in the presence of AlPO₄, phosphoric acid and water (cf. Journ.Am. Chem. Soc. 76 (1954), 5951). The same applies to the system Al(OH)₃·H₃ PO₄ and water (cf. Bull. Soc. chim. France (1961), 2285).

Owing to the fact that a relatively long period of time, from severalweeks to several months is necessary to obtain even small quantities ofAlH₃ (PO₄)₂ ·3H₂ O, these methods of preparation are not practical.

The AlH₃ (PO₄)₂ ·3H₂ O is a valuable accelerator for settinghydraulically settable mixtures of building materials, therefore, aneconomically attractive process for preparing it was desired.

The present invention is particularly directed to a method of makingcrystalline AlH₃ (PO₄)₂ ·3H₂ O which comprises first preparing asolution of water, an organic solvent miscible with water and aluminumphosphate having a molar ratio of Al₂ O₃ :P₂ O₅ in the range of 1:2 to1:6, subsequently crystallizing AlH₃ (PO₄)₂ ·3H₂ O from said solutionand recovering said AlH₃ (PO₄)₂ ·3H₂ O.

The aqueous solution from which the AlH₃ (PO₄)₂ ·3H₂ O is crystallizedmay be prepared by various different procedures. For example, an aqueoussolution of aluminum phosphate may be prepared and the organic solventslowly added thereto; crystalline Al(H₂ PO₄)₃ may be dissolved in anorganic solvent, such as ethanol to obtain an aluminum phosphate solventsolution and water slowly added thereto; and Al(OH)₃ can be reacted inan organic solvent with phosphoric acid to form a solution of aluminumphosphate, water and organic solvent.

Aqueous aluminum phosphate solutions can be obtained by reacting Al(metallic), Al₂ O₃ and Al(OH)₃ with phosphoric acid containing water;and aqueous-organic solvent-aluminum phosphate solutions can be preparedby reacting Al (metallic), Al₂ O₃ and Al(OH)₃ with phosphoric acid(containing water) in an organic solvent.

The preparation of the solutions from which the AlH₃ (PO₄)₂ ·3H₂ O iscrystallized is preferably carried out in such a manner that noimmediate precipitate is formed, for example as the organic solvent isslowly, i.e. gradually added to an aqueous aluminum phosphate solution.A rapid addition of the organic solvent to the aqueous aluminumphosphate solution may produce precipitation of amorphous aluminumphosphates. The solution of water, an organic solvent miscible withwater and aluminum phosphate after preparation can exist as such for asignificant period of time, for example 1-2 hours, prior to thecommencement of crystallization of AlH₃ (PO₄)₂ ·3H₂ O taking place.

The term aluminum phosphate as used herein is intended to include thealuminum salts of orthophosphoric acids, and the acid salts thereof.

The crystallization which normally takes place in several days, forexample about 6 to 8 days, can be enhanced and appreciably acceleratedby the addition of crystalline AlH₃ (PO₄)₂ ·3H₂ O seed crystals in whichcase the crystallization can take place in 12 to 24 hours.

The order in which the water, organic solvent, aluminum phosphate andseed crystals are brought together to form the solution from whichcrystallization takes place is not particularly critical except that itis necessary that the materials with the exception of the seed crystalsform a solution. For example, the seed crystals can be added to anaqueous aluminum phosphate solution and the organic solvent can be addedthereto; the organic solvent can be added to an aqueous aluminumphosphate solution and the seed crystals added thereto; and the seedcrystals can be added to the organic solvent and the solvent added to anaqueous aluminum phosphate solution. The AlH₃ (PO₄)₂ ·3H₂ O seedcrystals are difficulty soluble in aqueous aluminum phosphate and in theorganic solvent and normally do not go into solution.

A preferred method of the present invention comprises preparing thesolution of aluminum phosphate and water, slowly, i.e. gradually addingan organic solvent miscible with water thereto while stirring to obtainthe solution, adding seed crystals and crystallizing AlH₃ (PO₄)₂ ·3H₂ Ofrom said solution.

It was found that if the organic solvent is added too rapidly there is arisk that an amorphous aluminum phosphate precipitate is obtained. Therequired slow rate of addition of the organic solvent can be determinedby a simple test run. An especially pure final product can be obtainedby, after the addition of the organic solvent, filtering the resultingsolution to remove any small amounts of amorphous aluminum phosphatesthat may have inadvertently been formed, adding the seed crystals to thefiltrate and then carrying out the crystallization step.

According to the present invention AlH₃ (PO₄)₂ ·3H₂ O may be readilyprepared with excellent yields of more than 90% of theoretical yield. Amolar proportion of Al₂ O₃ :P₂ O₅ of from about 1:2 to 1:6, preferablyabout 1:2.5 to 1:3.2 and more preferably of about 1:3 can be used. Inthe latter case Al(H₂ PO₄)₃ may be used as a starting material and maybe reacted with water and solvents, whereby a reaction according to thefollowing equation takes place.

    Al(H.sub.2 PO.sub.4).sub.3 + 3H.sub.2 O→AlH.sub.3 (PO.sub.4).sub.2 · 3H.sub.2 O + H.sub.3 PO.sub.4

or isolating Al(H₂ PO₄)₃ may be advantageously dispensed with, becauseits preparation is very complicated. It is quite sufficient to startwith solutions of a similar composition (e.g. having the same molarproportion of Al₂ O₃ /P₂ O₅,i.e. of about 1:3) which may be easilyprepared, e.g. from aluminum hydroxide and phosphoric acid and to addwater miscible, i.e. soluble organic solvents thereto. Startingsolutions having other molar proportions of Al₂ O₃ /P₂ O₅ may also beused.

The reaction time required according to the aforesaid process may befurther reduced by slightly increasing the reaction temperature. Thetemperature, however, is not a critical factor. The process may becarried out at all temperatures, at which water or organic solventsneither solidify nor boil. Temperatures of from 15° to 50° C areadvantageous. Temperatures of from 30° to 40° C are especiallyadvantageous.

It is surprising that the desired phosphate AlH₃ (PO₄)₂ ·3H₂ O may beprepared from Al(H₂ PO₄)₃ according to the process of the invention,since it is known that Al(H₂ PO₄)₃ crystals are extremely sensitive tohumidity, deliquesce in air giving a clear, viscous liquid and dissolvein a small quantity of cold water to yield a completely clear solutionwithout forming AlH₃ (PO₄)₂ ·3H₂ O. It is therefore surprising thatyields of AlH₃ (PO₄)₂ ·3H₂ O of more than 90% of the theory are obtainedby the addition of the organic solvent.

A small quantity of water is required to permit growing of the AlH₃(PO₄)₂ ·3H₂ O crystals in the mother liquor. The yield of the aforesaidproduct, however, decreases with an increasing water content. It istherefore advantageous to start with highly concentrated aluminumphosphate solutions. The preferred aqueous aluminum phosphate solutioncontain 50 to 85.5% by weight of aluminum phosphate, for example asAl(H₂ PO₄)₃.

Large excesses of free phosphoric acid cause a reduction of the yield ofAlH₃ (PO₄)₂ ·3H₂ O. It is therefore advantageous to start with aluminumphosphate solutions having an atomic ratio of Al/P of from about 1:2 to1:3 since, in this case, relatively little phosphoric acid willaccumulate in the mother liquor in the course of the crystallizationprocess.

Examples of suitable solvents are those miscible with water to anunlimited extend. Alcohols having from 1 to 3 carbon atoms, carboxylicacids having from 1 to 3 carbon atoms, acetonitrile, acetone, dioxaneand tetrahydrofurane have proved advantageous. Ethanol has provedespecially advantageous.

Glycerin cannot be used perhaps due to the fact that the high viscosityof the solution considerably slows down the growing of the crystals. Aseries of solvents miscible with pure water to an unlimited extent formtwo liquid phases with the aluminum phosphate solution, but afterprecipitation of the crystalline AlH₃ (PO₄)₂ ·3H₂ O one liquid phase isonly present, for example in the case of tetrahydrofurane andisopropanol.

Solvents miscible with water to a limited extent may also be used. Ithas become evident that solvents having a solubility in water in roomtemperature of about 1 to 10% may be used. Among these solvents theremay be mentioned, for example ketones having from 4 to 6 carbon atomssuch as methyl isobutyl-ketone or cyclohexanone, carboxylic acid alkylester having from 2 to 4 carbon atoms, such as for example methyl orethyl formiate or methyl acetate and aliphatic alcohols having from 4 to6 carbon atoms such as isoamyl alcohol or cyclohexanol.

Solvents boiling at a temperature below 100° C are advantageous for aneasier recovering of the organic solvent by distillation.

A suitable solvent added in the crystallization process generally shouldhave the following characteristics:

a. It should dissolve Al(H₂ PO₄)₃ readily.

b. It should readily dissolve the byproduct H₃ PO₄ formed.

c. It should not dissolve AlH₃ (PO₄)₂ ·3H₂ O and thus act as aprecipitating agent.

d. It should be well miscible with H₂ O.

e. It should reduce the viscosity of the solution.

The optimal quantity of the solvent added depends on the water contentof the aluminum phosphate solution and of the relation Al₂ O₃ :P₂ O₅.The greater the content of free phosphoric acid and unreacted water, themore organic solvent is required for improving the yield. Amounts offrom 40 to 90% by volume of organic solvent based on total solution haveproved advantageous. Especially in the case of ethanol the quantities oforganic solvent to be added range of from 50 to 400 ml/mole of residualphosphoric acid.

However, if excessive amounts of organic solvents miscible with water toan unlimited extent are used, significant amounts of undesirableamorphous aluminum phosphate precipitates may form. The risk of formingamorphous precipitates is substantially eliminated by adding only from66 to 100% by volume of solvent, based on the volume of aqueous aluminumphosphate solution. On the other hand, there is substantially littlerisk of forming amorphous precipitates when using organic solvents whichare miscible with water to a limited extent.

An especially advantageous method of the process according to theinvention consists in recycling the mother liquors to the process aftertreating them so that a complete conversion is obtained.

In the preparation of AlH₃ (PO₄)₂ ·3H₂ O from crystallized Al(H₂ PO₄)₃according to the equation:

    Al(H.sub.2 PO.sub.4).sub.3 + 3H.sub.2 O→ AlH.sub.3 (PO.sub.4).sub.2 ·3H.sub.2 O + H.sub.3 PO.sub.4

the mother liquor obtained is a mixture of H₃ PO₄, water and the organicsolvent. The solvent is distilled off and recycled to the process. Theremaining water containing H₃ PO₄ may be reused for preparing thealuminum phosphate starting material. In the preparation of AlH₄ (PO₄)₂·3H₂ O from an aluminum phosphate solution having approximately thecomposition Al₂ O₃ :P₂ O₅ = 1:3 according to the equations ##EQU1## inthe presence of an organic solvent miscible with water, the motherliquor obtained is a solution wherein the complete quantity of water ofthe originally used diluted H₃ PO₄ is accumulated.

The organic solvent is advantageously distilled off and recycled to theprocess. The remaining diluted H₃ PO₄ may be reused as follows:

a. H₃ PO₄ is concentrated up to the original content by distilling offthe excess of water and is recycled to the process.

b. The original concentration of unconsumed H₃ PO₄ is obtained by addingP₂ O₅ or highly concentrated H₃ PO₄ and H₃ PO₄ is reused.

c. The diluted H₃ PO₄ is used for producing further products (forexample complex fertilizers), wherein the low content of aluminumphosphate does not matter.

AlH₃ (PO₄)₂ ·3H₂ O is a white, finely crystalline powder resistant tohumid atmospheres.

It has been found that AlH₃ (PO₄)₂ ·3H₂ O can be used as an acceleratorfor the setting of hydraulically settable mixtures of building materialssuch as methyl cellulose containing premixed plasters and flooringplaster materials, preferably cement bound.

It is already known that the setting and, consequently, the hardening ofcement and other hydraulic binders may be accelerated by the addition ofvarious chemicals.

Additions of chlorides such as calcium or aluminum chloride, alkalisilicates, alkali carbonates and alkali phosphates are often used forthis purpose.

These additions generally have certain disadvantages; the chlorides, forexample, stimulate corrosion, the alkali salts increase the content ofwater soluble satls and cause efflorescences.

It has been proved that the setting process, for example, of methylcellulose containing hydraulically setting premixed plasters may beessentially accelerated without any inconvenience by adding to theplaster mixture a small quantity of finely divided acid aluminumphosphate of the formula AlH₃ (PO₄)₂ ·3H₂ O. This addition isadvantageously maintained in the range of from 0.02 to 10% calculated onthe hydraulic binder or of from 0.05 to 5% calculated on the dry mixtureof building material.

It has been proved that the time required till the beginning of thesetting of the hydraulic binder when not using an addition of AlH₃(PO₄)₂ ·3H₂ O can be reduced half or up to a quarter or less dependingon the quantity of the addition of AlH₃ (PO₄)₂ ·3H₂ O.

The following data show the effect obtained by the addition of acidaluminum phosphate according to the invention, the setting time of alime-cement plaster without or with methyl cellulose being determined bymeans of the Vicat conus apparatus (DIN 1168). This measuring method waschosen in accordance with the treating method of premixed plastersmechanically applied in a single coat.

    ______________________________________                                        Plaster mixture consisting of:                                                                       Time of Setting:                                       ______________________________________                                        200 p.b.w. of Portland cement                                                 100 p.b.w. of white lime hydrate                                              700 p.b.w. of quartz sand of from                                             0 to 0.6 mm                                                                   without addition of accelerator                                                                      about 290 minutes                                      with the addition of                                                          1 p.b.w. of methyl cellulose                                                                         about 330 minutes                                      without the addition of methyl cellulose                                      but with the addition of 5 p.b.w. of                                          Al.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                                                               about  75 minutes                                      with the addition of                                                          1 p.b.w. of methyl cellulose                                                  5 p.b.w. of Al.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                                                   about  90 minutes                                      ______________________________________                                    

From the aforesaid data it can be seen that the setting process isextremely accelerated by acid aluminum phosphate.

The process according to the invention may be advantageously used foraccelerating the setting process especially of such hydraulic plastermaterials containing nonionic cellulose ethers for the purpose ofimproving the adhesion and the water retention properties.

It is already known that said hydraulic binders show a considerableretardation of the setting process. Owing to the fact that the settingtime required for hydraulically bound plasters containing celluloseethers and processed by hand or mechanically is too long and theoperation process is considerably impeded, the addition of the aforesaidsetting accelerator offers real advantages. The finishing of theplasters can be effected after 1 to 2 hours whereas hydraulic plasterswhich have not been accelerated can only be smoothed after 4 to 5 hours.

The processibility of a plaster accelerated by acid aluminum phosphatecan be additionally improved by adding small amounts of from 0.01 to0.1% of an air entraining agent which additionally reduces the crackformation.

AlH₃ (PO₄)₂ ·3H₂ O may be used alone or combined with aluminumhydroxides or alkali phosphates for obtaining a determined settingcurve.

AlH₃ (PO₄)₂ ·3H₂ O or the combination thereof with further acceleratorsmay be added to the plaster mixture by grinding it with the binder or byadding it to the premixed plaster. When adding the substance to theprecast plaster a fineness of less than 100 μ is required in order toobtain a maximum effect.

Examples for using AlH₃ (PO₄)₂ ·3H₂ O in mixtures of building materialsare as follows:

    ______________________________________                                        EXAMPLE I                                                                     700 p.b.w.  of sand (quartz or limestone sand) of                                         from 0 to 1 mm size                                               200 p.b.w.  of Portland cement                                                100 p.b.w.  of white lime hydrate                                             0.5 p.b.w.  of an air entraining agent                                        1.5 p.b.w.  of methyl hydroxyethyl cellulose                                  5.0 p.b.w.  of AlH.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                        EXAMPLE II                                                                    750 p.b.w.  of sand (quartz or limestone sand) of                                         from 0 to 1 mm                                                    250 p.b.w.  of highly hydraulic lime                                          0.5 p.b.w.  of an air entraining agent                                        1.5 p.b.w.  of methyl hydroxyethyl cellulose                                  5.0 p.b.w.  of AlH.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                        EXAMPLE III                                                                   700 p.b.w.  of sand (quartz or limestone sand) of                                         from 0 to 1 mm size                                               100 p.b.w.  of Portland cement clinkers                                       150 p.b.w.  of limestone flour                                                50 p.b.w.   of white lime hydrate                                             0.5 p.b.w.  of air entraining agent                                           1.5 p.b.w.  of methyl hydroxyethyl cellulose                                  0.5 p.b.w.  of AlH.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                        EXAMPLE IV                                                                    800 p.b.w.  of sand (quartz or limestone sand) of                                         from 0 to 1 mm size                                               200 p.b.w.  of Portland cement                                                0.5 p.b.w.  of air entraining agent                                           1.5 p.b.w.  of methyl hydroxyethyl cellulose                                  5.0 p.b.w.  of AlH.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                        EXAMPLE V                                                                     850 p.b.w.  of chalky sandstone reactor material                              100 p.b.w.  of Portland cement                                                50 p.b.w.   of lump slag                                                      0.5 p.b.w.  of air entraining agent                                           1.5 p.b.w.  of methyl hydroxyethyl cellulose                                  5.0 p.b.w.  of AlH.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                        EXAMPLE VI                                                                    300 p.b.w.  of Portland cement                                                700 p.b.w.  of sand of from 0 to 1 mm size                                    3 p.b.w.    of AlH.sub.3 (PO.sub.4).sub.2 . 3H.sub.2 O                        0.5 p.b.w.  of air entraining agent                                           ______________________________________                                    

The following examples illustrate the invention.

EXAMPLE 1:

78 g of Al(OH)₃ (= 1 mole) and 387 gms of a 76% H₃ PO₄ (= 3 moles of H₃PO₄) were mixed while stirring giving a suspension, which suspension wasthen heated while stirring to a temperature of from 35° to 40° C. Thetemperature of the reaction mixture then gradually increased due to thereaction heat without adding heat from the outside and reached from 105°to 110° C, whereby the reaction mixture considerably foamed for a shortperiod. A clear solution was obtained, otherwise a brief heating isrequired.

After cooling to 35° C AlH₃ (PO₄)₂ ·3H₂ O crystals were inoculated intothe solution while vigorously stirring and the solution was left overnight at a temperature of 35° C while frequently stirring. The reactionproduct was then cooled to room temperature, 200 ml of ethanol wereslowly introduced, i.e. gradually added, while stirring and the mixturewas allowed to stand for 24 hours while frequently stirring. Then it wasfiltered off with suction and centrifuged. The crystals obtained werewashed with alcohol in order to remove the adherent H₃ PO₄ and dried atthe air or in vacuo (at 25° C).

Yield of AlH₃ (PO₄)₂ ·3H₂ O : from 247 to 255 g = 90 - 95% of thetheory.

EXAMPLE 2

50 gms of Al(H₂ PO₄)₃ were mixed by stirring with 50 ml of ethanolgiving a syrup and 25.5 mls of H₂ O were slowly introduced, i.e.gradually added. Thereafter the syrup was inoculated with AlH₃ (PO₄)₂·3H₂ O crystals and left for 6 days at a temperature of about 20° Cwhile frequently stirring. The crystalline slurry was then filtered offwith suction, impressed on a clay plate and dried in air after washingit with ether or alcohol. Yield of AlH₃ (PO₄)₂ ·3H₂ O : 41 g = 95% ofthe theory.

EXAMPLE 3

The example was carried out as example 2, but by using acetone insteadof ethanol and the mixture was treated as described in example 2.

Yield of AlH₃ (PO₄)₂ ·3H₂ O : 39 g = 91% of the theory.

EXAMPLE 4

The starting mixture prepared was the same as in example 2, but thereaction mixture was allowed to stand at a temperature of from 25° to40° C after inoculating it. It could already be treated after 4 daysaccording to example 2. Yield of AlH₃ (PO₄)₂ ·3H₂ O : 40 g = 93% of thetheory.

EXAMPLE 5

78 g of Al(OH)₃ were mixed by stirring with 200 mls of ethanol and 387gms of phosphoric acid of 76% concentration were slowly added.Thereafter the temperature of the reaction mixture increased within 1hour to 50° C without adding heat from the outside. The reaction mixturewas heated and refluxed for about 10 minutes (interior temperature 83°C). The resulting product was cooled and insoluble products werefiltered off. 100 mg of seeding crystals of AlH₃ (PO₄)₂ ·3H₂ O wereadded and the reaction mixture was allowed to stand for 24 hours at atemperature of 35° C while frequently stirring. After suction-filtering252 g of crystalline AlH₃ (PO₄)₂ ·3H₂ O were obtained.

EXAMPLE 6

The example was performed in the same manner as in Example 5 but withoutadding seeding crystals. About 200 g of crystalline AlH₃ (PO₄)₂ ·3H₂ Ohad precipitated after 8 days.

What is claimed is:
 1. A process for preparing crystalline AlH₃ (PO₄)₂·3H₂ O by crystallization from an aqueous solution which comprises firstpreparing a solution containing water, an organic solvent miscible withwater and aluminum phosphate having a molar ratio of Al₂ O₃ :P₂ O₅ offrom 1:2 to 1:6, and subsequently crystallizing AlH₃ (PO₄)₂ ·3H₂ O fromsaid solution, and recovering crystalline AlH₃ (PO₄)₂ ·3H₂ O.
 2. Theprocess of claim 1 wherein AlH₃ (PO₄)₂ ·3H₂ O seed crystals are added tosaid solution to enhance crystallization of AlH₃ (PO₄)₂ ·3H₂ O from saidsolution.
 3. The process of claim 1 wherein the organic solvent is amember selected from the group consisting of alcohols having from 1 to 3carbon atoms, carboxylic acids having from 1 to 3 carbon atoms,acetonitrile, acetone, dioxane and tetrahydrofurane.
 4. The process ofclaim 1 wherein the organic solvent is a member selected from the groupconsisting of ketones having from 4 to 6 carbon atoms, carboxylic acidesters having from 2 to 4 carbon atoms and aliphatic alcohols havingfrom 4 to 6 carbon atoms.
 5. The process of claim 1 wherein the solventis a member selected from the group consisting of methyl isobutylketone,cyclohexanone, methyl formiate, ethyl formiate, methyl acetate, isoamylalcohol and cyclohexanol.
 6. A process for preparing crystalline AlH₃(PO₄)₂ ·3H₂ O from an aqueous aluminum phosphate solution, whichcomprises preparing an aluminum phosphate and water solution having amolar ratio of Al₂ O₃ :P₂ O₅ of from 1:2 to 1:6, and slowly adding tosaid solution an organic solvent miscible with water, crystallizing saidAlH₃ (PO₄)₂ ·3H₂ O from solution and separating crystalline AlH₃ (PO₄)₂·3H₂ O from solution.
 7. The process of claim 6 wherein the aluminumphosphate solution is obtained by reacting aluminum hydroxide andphosphoric acid.
 8. The process of claim 6 wherein the solutioncomprises Al(H₂ PO₄)₃.
 9. The process of claim 6 wherein 40 to 90% byvolume of an organic solvent, based on total aluminum phosphate, waterand solvent solution, is added to the aqueous solution.
 10. The processof claim 6 wherein 50 to 400 mls. of organic solvent per mole ofresidual phosphoric acid are added to the aqueous solution.
 11. Theprocess of claim 1 wherein an aluminum compound and phosphoric acid arereacted in an organic solvent miscible with water to form an aluminumphosphate, water and organic solvent solution, and crystallizing AlH₃(PO₄)₂ ·3H₂ O from said solution.
 12. The process of claim 11 whereinaluminum hydroxide and phosphoric acid are reacted in the organicsolvent to obtain aluminum phosphate and water.
 13. The process of claim11 wherein AlH₃ (PO₄)₂ ·3H₂ O seed crystals are added to the solution toenhance crystallization of the AlH₃ (PO₄)₂ ·3H₂ O from said solution.14. The process of claim 11 wherein aluminum hydroxide is added to theorganic solvent and subsequently phosphoric acid is added to the solventto form aluminum phosphate and water.
 15. The process of claim 1 whereinaluminum hydroxide is added to an organic solvent comprising ethanol,phosphoric acid is subsequently added and reacted with the aluminumhydroxide to form a water, organic solvent, aluminum phosphate solution,AlH₃ (PO₄)₂ ·3H₂ O seed crystals are added and AlH₃ (PO₄)₂ ·3H₂ O iscrystallized from the solution.
 16. A process for preparing crystallineAlH₃ (PO₄)₂ ·3H₂ O, which comprises preparing an aqueous solution of analuminum phosphate having a molar ratio of Al₂ O₃ :P₂ O₅ of from 1:2 to1:6, slowly adding to said solution an organic solvent miscible withwater, crystallizing said AlH₃ (PO₄)₂ ·3H₂ O from solution andrecovering about 90% theoretical yield of crystalline AlH₃ (PO₄)₂ ·3H₂O.
 17. The process of claim 6, wherein the organic solvent is a memberselected from the group consisting of alcohols having from 1 to 3 carbonatoms, carboxylic acids having from 1 to 3 carbon atoms, acetonitrile,acetone, dioxane and tetrahydrofurane.
 18. The process of claim 6,wherein the organic solvent is a member selected from the groupconsisting of ketones having from 4 to 6 carbon atoms, carboxylic acidesters having from 2 to 4 carbon atoms and aliphatic alcohols havingfrom 4 to 6 carbon atoms.
 19. The process of claim 6, wherein thesolvent is a member selected from the group consisting of methylisobutylketone, cyclohexanone, methyl formiate, ethyl formiate, methylacetate, isoamyl alcohol and cyclohexanol.
 20. The process of claim 6,wherein the aqueous solution comprises an aluminum phosphate.
 21. Aprocess for preparing crystalline AlH₃ (PO₄)₂ ·3H₂ O by crystallizationfrom an aqueous solution which comprises preparing a solution containingwater and aluminum phosphate having an aluminum phosphate concentrationof 50 to 85.5% by weight and having a molar ratio of Al₂ O₃ :P₂ O₅ offrom 1:2 to 1:6, slowly adding to said solution an organic solventmiscible with water to form a solvent-solution mixture wherein saidsolvent is a member selected from the group consisting of alcoholshaving from 1 to 3 carbon atoms, carboxylic acids having from 1 to 3carbon atoms, acetonitrile, acetone, dioxane and tetrahydrofurane, saidsolvent comprising about 40 to 90% by volume of said solvent-solutionmixture, crystallizing AlH₃ (PO₄)₂ ·3H₂ O from solution and recoveringcrystalline AlH₃ (PO₄)₂ ·3H₂ O therefrom.
 22. The process of claim 21,wherein the molar proportion of Al₂ O₃ :P₂ O₅ is about 1:2.5 to 1:3.2.23. The process of claim 21, wherein the crystallization is carried outat a temperature of about 15° to 50° C.
 24. A process for preparingcrystalline AlH₃ (PO₄)₂ ·3H₂ O by crystallization from an aqueoussolution which comprises preparing a solution containing water andaluminum phosphate having a molar ratio of Al₂ O₃ :P₂ O₅ of from 1:2 to1:6, slowly adding to said solution an organic solvent having asolubility in water at room temperature of about 1 to 10%, wherein saidorganic solvent is a member selected from the group consisting ofketones having from 4 to 6 carbon atoms, carboxylic acid esters havingfrom 2 to 4 carbon atoms and aliphatic alcohols having from 4 to 6carbon atoms and crystallizing AlH₃ (PO₄)₂ ·3H₂ O from solution.
 25. Theprocess of claim 24 wherein the molar proportion of Al₂ O₃ :P₂ O₅ isabout 1:2.5 to 1:3.2.
 26. The process of claim 24 wherein thecrystallization is carried out at a temperature of about 15° to 50° C.